Institutional and consumer automatic dishwashers or warewashing machines typically provide two or more stages which include various combinations of a soak, a prewash, a main wash, a rinse, a sanitizing cycle and a drying cycle.
Dishes washed in automatic dishwashers or warewashing machines are preferably obtained without food soils and without residue from the cleaning solutions or other chemical(s) used in the washing process. One type of residue, known as streaking and spotting, is common on machine washed dishes. Streaking and spotting is believed to result when water remains attached to the dishes after the rinse cycle and then evaporates from the surface of the dishes.
Rinse agents are commonly added to rinse water in an effort to reduce the surface tension of the rinse water and thereby promote sheeting of the water from the dishes. Typical rinse aid formulas require a solution concentration of about 1000 ppm to provide efficient sheeting and drying.
Rinse aids are currently available in liquid or solid form. Solid rinse aids are generally preferred for a variety of reasons including manufacturing cost, manufacturing and dispensing convenience, and dispensing safety. In addition, dispenser units for solid rinse aids tend to be less expensive and more durable because they require fewer moving parts.
One of the difficulties encountered in the use of a rinse aid is that the rinse cycle is typically the last cycle in the warewashing process which permits solubilized particles of the rinse agent to remain on the cleaned dishes. Because of the obvious possibility for ingestion of residual rinse aid, it is desirable that such residue be of food grade quality.
Typical liquid rinse aids are disclosed in Japanese Application Nos. 48-38588 and 48-112123. Japanese Application No. 48-38588 discloses a liquid rinse agent which includes a sucrose acid ester, a sorbitan acid ester, a monohydric alcohol such as ethanol, a polyhydric alcohol such as ethylene glycol, and optionally water. Japanese Application No. 48-112123 discloses a liquid rinse aid which includes a major proportion of a sorbitan ester, a minor proportion of a monohydric or polyhydric alcohol, and optionally an aliphatic acid and/or water. While such liquid rinse agents are generally effective for preventing streaking and spotting, they suffer from the general drawbacks associated with liquid rinse agents and further suffer from uncontrollable excessive consumptions of the rinse agent due to the relatively high solubility of the compound.
Many of the currently available solid rinse aids contain a polyalkylene oxide surfactant which is commonly a polyoxyethylene-polyoxypropylene block copolymer. Some of these polyoxyethylene-polyoxypropylene block copolymer, while generally effective for preventing streaking and spotting, can coagulate within the dishwashing machine at elevated temperatures. Such coagulation of the block copolymer enhances the ability of the copolymer to remain attached to the surface of the dishes during the rinse cycle and thereby encourages retention of the rinse agent on the clean dishes and can cause visible spotting upon the dishes.
Accordingly, a substantial need exists for a solid, concentrated, food grade, rinse aid which is effective for eliminating spotting and streaking at relatively low solution concentrations and provides a controllable dispensing rate.